Magnetic recording medium and method of forming the same and magnetic disk drive

ABSTRACT

A magnetic recording medium having magnetic patterns into which servo information are written and a magnetic recording layer into which data are written comprises a nonmagnetic substrate, a magnetic recording layer formed on the substrate, and a hard magnetic layer contacted the magnetic recording layer within servo signal recording regions on the substrate and constituting servo patterns of film thicknesses of which are varied in the track length direction. Thereby, more precise reading of the servo signals by the magnetic head is assured and a surface of the magnetic recording medium can be flatted.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a magnetic recording medium and amethod of forming the same and a magnetic disk drive and, moreparticularly, a magnetic recording medium having magnetic patterns intowhich servo information (track position information) are written and amagnetic recording layer into which data are written and a method offorming the same and a magnetic disk drive which is equipped with themagnetic recording medium.

2. Description of the Prior Art

In order to enhance a magnetic recording density, there is a tendency toincrease a track density of the magnetic recording medium (magneticdisk) in the field of the magnetic disk drive. Improvements in trackingaccuracy of the magnetic head are indispensable for accomplishing thehigh track density. Various tracking servomechanisms such as servosurface servomechanism, sector servomechanism, buried servomechanism, orthe like may be considered as a means for detecting the trackingposition.

In these servomechanisms, servo signals written into the magnetic diskare read by means of the magnetic head, and a head actuator iscontrolled based on the servo signals to shift the magnetic head to atarget track position.

As the magnetic recording medium having a structure for recording boththe servo signals and data information, as set forth in Japanese PatentApplication Publication (KOKAI) 2-218016, for instance, there has beenproposed such a method that uneven bits to be read magnetically areprovided on the surface of the magnetic recording medium, then magneticfluxes generated from ends of the bits are detected as tracking signals,and then position of the magnetic head is controlled based on thetracking signals. The structure with the magnetic recording layer on thebits and the structure without the magnetic recording layer on the bitshave been proposed.

However, the presence of the uneven surface of the magnetic recordingmedium prevents the magnetic head from being in a lower flying heightstate over the magnetic disk. Such uneven surface causes trouble if ahigh recording density should be achieved by decreasing the flyingheight of the magnetic head. Moreover, if the magnetic disk has anuneven surface, dusts are easily accumulated in concave portions on theuneven surface of the magnetic recording medium. On the other hand, inJapenese Patent Application Publications (KOKAIs) 59-72644 and 4-34718,there has been set forth that a magnetic recording medium having thestructure wherein magnetic substance patterns (referred to as "servopatterns" hereinafter) for recording servo information therein areformed on the substrate, and then the nonmagnetic layer and the magneticrecording layer are formed on the servo patterns and the substrate insequence.

In Japenese Patent Application Publication (KOKAI) 4-34718, there hasbeen set forth that the servo patterns are to be formed by a lift-offmethod, thereby improving surface evenness of the magnetic recordinglayer.

However, according to the structures of the servo patterns set forth inthese publications (KOKAIs), the servo patterns and the magnetic headare positioned at a good distance away since not only a gap due to theflying height of the magnetic head but also the nonmagnetic layer andthe magnetic recording layer are present between the servo patterns andthe magnetic head. For this reason, read error of the servo signalseasily occurs because, with the longer distance between the servopatterns and the magnetic head, the signal magnetic fields generatedfrom the servo patterns to the magnetic head is lessened.

If the lift-off method is utilized to form the servo patterns, flashesare prone to be formed around peripheries of the servo patterns. Theoccurence of flashes increases the likehood of a head crash of themagnetic head in the low flying height region. In order to achieve hightrack density, the precision of tracking the magnetic head has to beimproved. For example, the phase servo system has been used to detectinformation with regard to the tracking position.

The phase servo system is that the servo patterns are arranged to changethe phase of the reproduced servo signal according to position of themagnetic head in the track direction (circumferential direction).

In the prior art, in order to record such servo patterns on the surfaceof the magnetic recording medium, a following method has been employed.For instance, as shown in FIG. 1A, while the magnetic head 120 is beingshifted in the width direction of the track 110 by the first pitch L1having a length which can be divided into plural lengths (e.g., three tofour lengths) in the width direction (diameter direction) of the track110 and concurrently the magnetic head 120 is being shifted by thesecond pitch L2 in the circumferential direction, a plurality ofmagnetization inversion patterns are formed on the surface of themagnetic recording medium. The magnetization inversion patterns areutilized as the servo patterns 130. A width of magnetic pole of arecording inductive head of the magnetic head 120 is almost identical tothe track width.

The precision of detecting the tracking (track alignment) information inthe phase servo system becomes higher as the number of split in eachtrack in the diameter direction is increased larger. Such precision alsobecomes higher as the servo patterns 130 are made more sharply.

However, the more the number of split in each track 110, the more therecording time of the servo patterns 110 per one sheet of the magneticrecording medium. Further, if the number of split in each track 110 isincreased, the alignment precision of the magnetic head 120 is reducedin the high density track upon recording the servo patterns 130. Stillfurther, as shown in FIG. 1B, because of leakage magnetic fieldgenerated from end portions of the magnetic pole of the magnetic head120, bit bends 131 occur at the end of the servo pattern 130. Otherwise,because of recording bleeding, erase regions 132 occur at the end of theservo pattern 130. As a result, there is such a problem that the qualityof servo information is debased.

Since small servo patterns per bit, as set forth in Patent ApplicationPublication (KOKAI) 59-72644, are formed in plural numbers within onetrack, omissions of such patterns would be caused upon etching to formthe servo patterns.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a magnetic recordingmedium capable of ensuring more precise reading of servo signals by amagnetic head and also improving surface evenness of the magneticrecording medium, a method of manufacturing the same capable ofimproving surface evenness of the magnetic recording medium stillfurther, and a magnetic disk drive which is equipped with the magneticrecording medium.

According to the present invention, since film thicknesses of the hardmagnetic layer formed successively so as to contact the magneticrecording layer are varied in the track length direction within theservo signal recording region and the thicker portions of the hardmagnetic layer are used as the servo patterns.

Consequently, because a distance between the servo patterns and themagnetic head can be reduced extremely, the servo signal magnetic fieldsread by the magnetic head are enhanced, and therefore read error can beprevented from being generated.

As the first structure of the magnetic recording medium wherein the filmthickness of the hard magnetic layer is varied in the servo signalrecording region, first, there is a structure wherein the servo layersmade of hard magnetic substance are formed beneath the magneticrecording layer made of hard magnetic substance. In this event, theservo signals are written into the servo layers as well as the magneticrecording layer to thus increase intensity of the servo signal magneticfields. Besides, the servo layer constitutes a plurality of servopatterns if patterned. When a surface of the magnetic recording mediumopposing to the magnetic head is planalized by forming the nonmagneticlayer beneath the magnetic recording layer so as to surround the servopatterns, the magnetic head can be prevented previously from beingcrashed in a low flying height state.

As the second structure of the magnetic recording medium, there is astructure wherein the servo layers made of hardy magnetic substance aresuperposed on the magnetic recording layer made of hard magneticsubstance. In this case, the servo signals are written into the servolayers as well as the magnetic recording layer to thus increaseintensity of the magnetic fields caused by the servo signals. Further,the servo layer constitutes a plurality of servo patterns if patterned.If the nonmagnetic layer is formed on the magnetic recording layer so asto surround the servo patterns, the surface of the magnetic recordingmedium opposing to the magnetic head is able to be flat.

In the case that the servo layer and the magnetic recording layer areformed by the same substance, it has been confirmed experimentally thatthe tracking information magnetic field having the same magnitude as thedata signal magnetic field can be derived if the film thickness of theservo layer is 2.5 or more times thicker than that of the magneticrecording layer. In other words, an amount of change in the filmthickness of the hard magnetic layer in the direction of the tracklength may be 2.5 or more times larger than the film thickness of themagnetic recording layer.

If the servo patterns are aligned in plural rows within each track tohave different phases and also are so formed in respective tracks thatthey are shifted to have different phases in the track length directiontrack by track, the tracking position information can be detected bydetecting displacement in waveforms of the tracking information magneticfields in the tracking length direction, which are caused due to phasedifference.

In the present invention, as the method of forming such servo patterns,after the servo patterns are formed by the lift-off method, the surfaceof the resultant structure is planalized by polishing or etching orburnishing. Therefore, surface evenness of the magnetic recording mediumcan be maintained, and generation of head crash can be preventedbeforehand.

As the different method of forming such servo patterns, after theconcave portions are formed on the nonmagnetic layer in the servopattern forming regions, the servo layers made of hard magneticsubstance and the planalization film are then formed on the nonmagneticlayer sequentially, and the servo layers and the planalization film arethen etched back, so that the servo patterns are formed with remainingthe servo layers only within the concave portions. According to thismethod, no flash occurs and surface evenness of the servo patterns andthe nonmagnetic layer is in no degree damaged.

As the still different method of forming such servo patterns, the hardmagnetic layer is formed, then the hard magnetic layers located in theservo pattern not-forming regions are changed into the nonmagneticlayers by ion-implanting nonmagnetic elements into the servo patternnot-forming regions, and then the remaining hard magnetic layers areused as the servo patterns. As a result, surface evenness of the servopatterns and their neighboring areas is in no ways damaged.

In case the structure is adopted wherein the servo patterns are stackedon the magnetic recording layer, after the hard magnetic layers areformed on the substrate, the hard magnetic layers in the servo patternnot-forming regions are thinned by etching, and then the nonmagneticlayer is stacked in the etched regions. Consequently, if the remainingthick hard magnetic layers being not subjected to etching are employedas the servo patterns, the nonmagnetic layers having the same thicknessas that of the servo pattern are formed around respective servopatterns. Therefore, surface evenness of the servo patterns and theirneighboring areas can be assured. If the hard magnetic layer in datawriting regions are thinned and such thin-layered hard magnetic layerare utilized as the magnetic recording layer, the servo patterns and themagnetic recording layer may be formed at a time. Therefore, man-hoursrequired for film forming in the magnetic recording medium can bereduced.

Another object of the present invention is to provide a magneticrecording medium on which servo patterns can be formed with highprecision to thus improve the precision of detecting the position, amethod of manufacturing the same and a magnetic recording apparatus.

According to another aspect of the present invention, since linear orcurved servo patterns are formed as physical patterns on the magneticrecording medium to cross over a plurality of tracks obliquely, neithererase region nor bit bend occur upon forming the servo patterns unlikethe prior art, thereby improving the precision of detecting theposition. In this event, since linear or curved servo patterns arearranged at an oblique angle, they are magnetically equivalent to theconventional servo patterns.

Such conventional servo patterns are recorded in one track only on amagnetic basis while being shifted by predetermined pitches in both thetrack width direction and the track length direction respectively.

The servo patterns of the present invention can be realized with the useof change in film thickness of the magnetic layer, change in unevennessof the magnetic layer, and partial use of the magnetic layer. Bycontinuously applying the magnetic field of the certain intensity fromthe outside to a plurality of such servo patterns along the certaindirection, servo information can be written into respective servopatterns. Servo information can be derived from change in the magneticfield.

In this manner, linear or curved servo patterns crossing over aplurality of tracks obliquely are simple, and therefore omissions ofpatterns are difficult to occur rather than the case servo patternswhich are obtained by dividing such servo patterns into plural parts arearranged. Further, such servo patterns can be formed by making use ofresist patterns. The resist patterns can be formed via exposure stepusing the exposure mask or laser beam irradiation.

In case latent images of the servo patterns are formed on the resist byusing the exposure mask, exposure is effected using one sheet ofexposure mask while the substrate for the magnetic recording mediumbeing rotated stepwise. In this case, provided that partial exposure ofthe resist performed every rotation step of the substrate is repeated,exposure process can be facilitated. Alternatively, alignment orfocusing of the exposure mask may be effected every time when rotationof the substrate is stopped.

Meanwhile, in case the resist is exposed by irradiating the laser beam,exposure process can be accelerated when exposure is conducted while thesubstrate on which the servo patterns are to be formed being rotatedstepwise or continuously.

Moreover, if the servo patterns are formed in the servo regions byetching the magnetic layer by the laser beam, servo patterns can beformed with good precision without exposure and development process forthe resist.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a plan view showing ideal servo patterns which are writtenone by one with a magnetic head in the prior art;

FIG. 1B is a plan view servo patterns which are actually written in theprior art;

FIG. 2 is a plan view showing an example of a magnetic disk drive havinga magnetic disk according to a first embodiment of the presentinvention;

FIG. 3 is a fragmental sectional view showing a magnetic recordingmedium according to a second embodiment of the present invention;

FIG. 4 is a plan view showing the magnetic recording medium according tothe second embodiment of the present invention in FIG. 3;

FIG. 5A is a fragmental plan view showing arrangement of servo patternsin the magnetic recording medium according to the second embodiment ofthe present invention in FIG. 3;

FIG. 5B is a waveform chart showing an example of tracking signalsobtained by reading the servo patterns in FIG. 5A by a magnetic head;

FIGS. 6A and 6B are schematic perspective views showing respectivelymethods of writing the tracking signals into the magnetic recordingmedium according to the second embodiment of the present invention;

FIG. 7A is a sectional view showing a method of reading the trackingsignals from the magnetic recording medium according to the secondembodiment of the present invention;

FIG. 7B is a characteristic view showing a relationship between thetracking signal and a film thickness of the servo patterns in FIG. 7A;

FIGS. 8A to 8E are sectional views illustrating a first method ofmanufacturing the magnetic recording medium according to the secondembodiment of the present invention;

FIGS. 9A to 9D are sectional views illustrating a second method ofmanufacturing the magnetic recording medium according to the secondembodiment of the present invention;

FIGS. 10A to 10D are sectional views illustrating a third method ofmanufacturing the magnetic recording medium according to the secondembodiment of the present invention;

FIG. 11 is a fragmental sectional view showing a magnetic recordingmedium according to a third Embodiment of the present invention;

FIGS. 12A to 12D are sectional views illustrating a first method ofmanufacturing the magnetic recording medium according to the thirdembodiment of the present invention; and

FIGS. 13A to 13D are sectional views illustrating a second method ofmanufacturing the magnetic recording medium according to the thirdembodiment of the present invention.

FIG. 14A is a plan view showing an example of servo patterns of themagnetic disk according to a fourth embodiment of the present invention;

FIG. 14B is an enlarged fragmental plan view of the example in FIG. 14A;

FIG. 15 is a sectional view showing a configuration of the magnetic diskaccording to the fourth embodiment of the present invention;

FIG. 16A is a perspective view showing an example wherein servoinformation are written into the magnetic disk according to the fourthembodiment of the present invention with a magnetic head;

FIG. 16B is a perspective view showing an example wherein servoinformation are written into the magnetic disk according to the fourthembodiment of the present invention with a permanent magnet;

FIG. 17 is a sectional view showing a mechanism where servo informationare read from the magnetic disk according to the fourth embodiment ofthe present invention and a waveform chart showing output waveforms fromthe magnetic head;

FIG. 18 is a plan view showing servo patterns to illustrate phase servoof the magnetic disk according to the fourth embodiment of the presentinvention and a waveform chart showing output waveforms from themagnetic head;

FIG. 19 is a plan view showing another example of servo patterns of themagnetic disk according to the fourth embodiment of the presentinvention;

FIG. 20A is a perspective view showing a first example of a resistexposure method upon forming servo patterns of the magnetic diskaccording to the fourth embodiment of the present invention;

FIG. 20B is a timing chart illustrating timings for step motor drive andlaser beam irradiation;

FIG. 21A is a perspective view showing a second example of a resistexposure method upon forming servo patterns of the magnetic diskaccording to the fourth embodiment of the present invention;

FIGS. 21B and 21C are timing charts illustrating timings for laser beamirradiation and step motor drive respectively;

FIGS. 22A to 22E are sectional views showing first steps formanufacturing the fourth magnetic disk according to the embodiment ofthe present invention;

FIG. 23 is a sectional view showing a second example of a configurationof the magnetic disk according to a fifth embodiment of the presentinvention;

FIGS. 24A to 24E are sectional views showing second steps formanufacturing a fifth magnetic disk according to the embodiment of thepresent invention;

FIGS. 25A and 25B are sectional views showing steps for manufacturing afirst example of a configuration of the magnetic disk according to asixth embodiment of the present invention; and

FIGS. 26A to 26C are sectional views showing steps for manufacturing asecond example of a configuration of the magnetic disk according to thesixth embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

There will be explained preferred embodiments of the present inventionhereinafter with reference to accompanying drawings.

First Embodiment

FIG. 2 is a plan view showing the inside of the magnetic disk drivehaving the magnetic disk (magnetic recording medium) according to anembodiment of the present invention.

In a housing 41 of a magnetic disk drive 40 shown in FIG. 2, a circulardisk type magnetic disk 1 or 42 is housed. A center of the magnetic disk1 or 42 is secured to a rotation shaft 1a of a spindle motor.

On a surface of a magnetic recording layer of the magnetic disk 1 or 42,a large number of tracks 44 are formed to be arranged in the radialdirection starting from the rotation center. Respective tracks 44 areformed to take annular regions which surround a periphery of therotation center. Furthermore, on the surface of the magnetic recordinglayer, servo regions 45 extending from the rotation center to theoutside in the radial direction are arranged in plural numbers in theperipheral direction. Although the tracks 44 and the servo regions 45are illustrated in FIG. 2 for easy understanding of the presentinvention, they do not actually appear on the surface of the magneticdisk 1 or 42.

A slider 46 equipped with the magnetic head is secured to the top end ofa head arm 47 and then positioned on the magnetic disk 1 or 42. Positionof the slider 46 can be changed on the magnetic disk 42 according to theswing of the head arm 47. The head arm 47 is secured to a rotation shaft10b of a step motor at its almost center portion. The head arm 47 ismoved along with the rotation shaft 10b which is rotated by a signalsupplied from a track control circuit 10a. In compliance with phasedifference in the tracking servo patterns in the servo regions 45, thetrack control circuit 10a may recognize the track position lying underthe magnetic head.

Second Embodiment

FIG. 3 is a fragmental sectional view showing a magnetic recordingmedium according to a second embodiment of the present invention. FIG. 4is a plan view showing the magnetic recording medium according to thesecond embodiment of the present invention in FIG. 3.

Referring to FIG. 3, a magnetic recording medium 1 comprises anonmagnetic substrate 2 made of an aluminum wafer covered by NiP, asilicon wafer, or a glass wafer, a magnetic recording layer 3 made of afirst hard magnetic substance such as CoCr, CoCrPt, CoCrTa, or CoNiCrformed on the nonmagnetic substrate 2, and a protection layer 4 forcovering the magnetic recording layer 3.

The magnetic recording medium 1 assumes the shape of the circular diskin which a shaft hole 1a is formed at the center thereof, and comprisesdata signal recording regions A and servo signal recording regions B, asshown in FIG. 4. The servo signal recording regions B is formed as thecircular arc shape, as shown in FIG. 4, so as to correspond to the swingorbit of the magnetic head H. This is because such circular arc shapemay reduce a difference in yaw angle caused between an inner peripheryand an outer periphery of the magnetic recording medium 1 when themagnetic head H is being swung by a rotary actuator 10b. If thedifference in yaw angle is increased, variation in the read signals readby the magnetic head H will be brought forth.

In the servo signal recording regions B of the surface of thenonmagnetic substrate 2, as shown in FIG. 3, a plurality of concaveportions 2a are formed at a distance to assume the servo pattern shape,and servo layers 5 made of a second hard magnetic substance such asCoCr, CoCrPt, CoCrTa or CoNiCr are buried in these concave portions 2a.One servo layer 5 in one concave portion 2a and the magnetic recordinglayer 3 formed on the servo layer 5 constitute substantially one servopattern 5p. Since the servo layers 5 contact the magnetic recordinglayer 3 in the servo signal recording regions B, servo information to bewritten into the servo layers 5 are also written into the magneticrecording layer 3 on the servo layers 5. Consequently, no data isrecorded in the magnetic recording layer 3 in the servo signal recordingregions B.

Either the same substance as the first hard magnetic substanceconstituting the magnetic recording layer 3 or different substance fromthe first hard magnetic substance may be used as the second hardmagnetic substance constituting the servo layers 5.

In the servo signal recording regions B, as shown in FIGS. 3 and 5A,stripe shape clock signal patterns 7 are buried on the surface of thenonmagnetic substrate 2. A distance between two clock signal patterns 7serves as one clock signal interval, and a plurality of servo patterns5p are arranged between two clock signal patterns 7 to assumesubstantially a matrix form.

In other words, a plurality of servo patterns 5p are aligned at acertain distance in the circumferential direction, i.e., the tracklength direction of the magnetic recording medium 1, but they arearranged in the diameter direction of the magnetic recording medium 1 toshift by a fixed amount α in every track length direction. If a rowpattern is defined by a plurality of servo layers 5 which are aligned inthe track length direction, a phase difference α appears, as shown inFIG. 5B, between signal magnetic field waveforms generated from twoadjacent row patterns.

In FIG. 5A, a size of the servo pattern 5p is so decided that two rowsof the servo patterns 5p can be arranged in one track width.

By detecting such phase difference α between the servo patterns 5p bythe magnetic head, a relative positional relationship between the trackposition in the magnetic recording medium 1 and the magnetic head H canbe detected. Accordingly, upon receiving the read signal from themagnetic head H, a control circuit 10 may shift the magnetic head H to atarget position via an actuator 10b.

Next, it will be explained hereinafter how to write tracking informationinto the servo patterns 5p.

Writing of tracking information may be carried out by means of eitherthe magnetic head H shown in FIG. 6A, or the permanent magnet P shown inFIG. 6B.

As shown in FIG. 6A, in the case of writing the tracking information bythe magnetic head H, under the condition where the magnetic recordingmedium 1 of the circular disk type is being rotated, the desired servolayers 5 and the magnetic recording layer 3 formed around the desiredservo layers 5 are magnetized in the circumferential direction (i.e.,track length direction) by a DC magnetic field generated from themagnetic head H to have the same magnetization direction. It ispreferable that, in writing the servo signal into the servo layers 5, arecording gap length Lg for the magnetic head H is longer than that usedwhen writing data into the magnetic recording layer 3 since a strongmagnetic field can be generated.

On the other hand, after an S pole and an N pole of the permanent magnetP are arranged along the circumferential direction, as shown in FIG. 6B,and then the magnetic recording medium 1 is rotated under suchcondition, the desired servo patterns 5p and the magnetic recordinglayer 3 around the servo patterns 5p are magnetized to have the samemagnetization direction.

According to either of the above methods of writing trackinginformation, both the servo patterns 5p and the clock signal patterns 7are magnetized in the same direction along the track length direction.Even if the data signal recording regions A are also magnetizedsimultaneously when the tracking information are written, such trackinginformation written into the data signal recording regions A may beerased by writing data thereinto.

The tracking information written as stated above are read via themagnetic head H having a magnetoresistance device 8 or inductive device9, as shown in FIG. 7A. In this case, since a substantial thickness ofthe servo patterns 5p is given by a sum of film thicknesses of the servolayer 5 and the magnetic recording layer 3, leakage servo magneticfields Hs leaked from the servo patterns 5p are increased in comparisonwith the case where the servo layer 5 and the magnetic recording layer 3are formed at a distance.

In addition, since the servo patterns 5p are formed on the same plane asthe magnetic recording layer 3, as shown in FIG. 7A, a distance betweenthe magnetic head H and the servo patterns 5p becomes substantiallyidentical to a distance between the magnetic head H and the magneticrecording layer 3. Therefore, servo magnetic field input into themagnetic head H is enhanced and the tracking information are able to beread more reliably.

In turn, an experimental result obtained by examining a relationshipbetween the tracking signal output read by the magnetic head H and thefilm thickness of the servo patterns 5p will be explained.

While running the servo patterns 5p on the track under the reproducingmagnetic head H, as shown in FIG. 7A, the tracking information have beenread to examine the relationship between the tracking signal output andthe film thickness of the servo patterns 5p. Consequently, the resultshown in FIG. 7B has been derived.

In FIG. 7B, an ordinate denotes tracking signal values which arenormalized by setting data signal output obtained from the magneticrecording layer 3 formed in the data signal recording region A to "1".In addition, if the film thickness of the magnetic recording layer 3 isassumed as "1" and then the number of laminated layer of the servo layer5 is set to N, the film thickness X of the servo layer 5 may be given byX=Nt (where t is a film thickness of the magnetic recording layer).

In FIG. 7B, with increase in the number of layer in the servo layer 5,the tracking signal is also increased. The tracking signal output havingthe same magnitude as the data signal output can be obtained if the filmthickness X of the servo layer 5 is about 2.5 times that of the magneticrecording layer 3. In case concave bits are provided on the magneticrecording layer 3 without the servo layer 5, the tracking signal outputderived from these bits becomes "0.5".

As evident from the above, the fact that the adjacent servo layers 5constituting the servo patterns 5p are formed at a distance would begiven as the reason why the servo signal output does not exceed the datasignal output unless the film thickness of the servo layer 5 becomes 2.5or more times thicker than that of the magnetic recording layer 3.

Subsequently, methods of forming the servo patterns 5p on the magneticrecording medium 1 as mentioned above will be explained.

FIRST EXAMPLE

First, as shown in FIG. 8A, a resist 11 is coated on the nonmagneticsubstrate 2, and then exposed and developed to form windows 12 incorresponding servo pattern forming regions within the servo signalrecording regions B.

Thereafter, as shown in FIG. 8B, areas of the nonmagnetic substrate 2exposed from the windows 12 of the resist 11 are etched to form concaveportions 2a therein. Ion milling, sputtering etching, chemical etching,etc. may be used as the etching method. However, if a physical etchingmethod (PVD method) such as ion milling is used, there is a possibilitythat flashes are formed on peripheries of the concave portions 2a.Therefore, it is mandatory to keep an appropriate ion irradiation angleto prevent such flashes.

If the silicon wafer is used as the nonmagnetic substrate 2, generationof such flashes can be prevented because reactive ion etching can beapplied to the silicon wafer.

Next, as shown in FIG. 8C, the servo layer 5 is formed on an entiresurface of the resultant structure by sputtering to be 5 to 250 nmthick. Subsequently, the resist 11 is peeled off by solvent to thusleave the servo layers 5 only in the concave portions 2a on thenonmagnetic substrate 2.

Then, as shown in FIG. 8D, the nonmagnetic substrate 2 and the servolayer 5 are planalized by means of mechanical polishing, ion milling, orsputtering. Since a recording surface of the magnetic recording medium 1being faced to the magnetic head is planalized by this planalizationprocess, there is no possibility that the magnetic head is lifted out ofthe recording face or the magnetic head which is sliding over therecording face is broken down by the projection.

After such planalization process, as shown in FIG. 8E, the magneticrecording layer 3 formed of CoCrPt and covering the servo layer 5 andthe nonmagnetic substrate 2 are formed by sputtering to have a thicknessof 5 to 100 nm, and then the protection film 4 is formed thereon, thuscompleting the magnetic recording medium having the structure shown inFIG. 3A.

SECOND EXAMPLE

First, as shown in FIG. 9A, the concave portions 2a are formed on thenonmagnetic substrate 2 by the method similar to the first example.

Next, as shown in FIG. 9B, the servo layer 5 made of CoCrPt is formed bysputtering on the nonmagnetic substrate 2 and within the concaveportions 2a to be 5 to 250 nm thick, and in turn the photoresist 15 iscoated on the servo layer 5.

After this process, as shown in FIG. 9C, if the photoresist 15 and theservo layer 5 are etched by virtue of ion milling, sputtering etching,or the like, the servo layers 5 remain only in the concave portions 2awhen the surface of the nonmagnetic substrate 2 is exposed.

In this event, mechanical polishing, or the like is not required sinceupper surfaces of the servo layers 5 in the concave portions 2a and theupper surface of the nonmagnetic substrate 2 are planalized.

In the next, as shown in FIG. 9D, the magnetic recording layer 3 formedof CoCrPt is formed on the servo layer 5 and the nonmagnetic substrate 2by sputtering to have a thickness of 5 to 100 nm. In addition, theprotection film 4 is formed on the magnetic recording layer 3. The servopatterns 5pare formed by both the servo layers 5 remaining in theconcave portions 2a and the magnetic recording layer 3 on the servolayers 5.

THIRD EXAMPLE

Although the servo patterns 5a formed according to the abovemanufacturing steps in the first example and the second exampleaforementioned are buried in the concave portions 2a formed on thesurface of the nonmagnetic substrate 2, servo patterns and a nonmagneticlayer may be formed on the nonmagnetic substrate 2 according tomanufacturing steps explained hereinbelow.

First, as shown in FIG. 10A, a hard magnetic layer 16 made of CoCrPt isformed on the nonmagnetic substrate 2 to be 5 to 250 nm thick.

Then, as shown in FIG. 10B, a resist 17 is applied on the hard magneticlayer 16, and then exposed and developed so as to expose the hardmagnetic layer 16 formed in regions except for servo pattern formingregions.

Subsequently, as shown in FIG. 10C, when chromium (Cr) is ion-implantedinto the hard magnetic layers 16 within the regions not covered by theresist 17, such hard magnetic layers 16 are changed into nonmagneticlayers 16a since the hard magnetic layers 16 formed within the ionimplantation regions become a Cr-rich state and also become a betteramorphous state. The hard magnetic layers 16 beneath the resist 17 andremaining in the servo pattern forming regions are used as the servopatterns 5p.

Since unevenness is not caused by ion-implantation on the surface of thehard magnetic layers 16, planalization process can be omitted.

As shown in FIG. 10D, after the resist 17 is removed, the magneticrecording layer 3 made of 5 to 100 nm thick CoCrPt is formed bysputtering to cover the servo patterns 5a and the nonmagnetic layers16a. Furthermore, the protection film 4 is formed on the magneticrecording layer 3, thereby finishing the magnetic recording medium.

In this structure, a plurality of servo patterns 5p directly contact themagnetic recording layer 3.

It would be understood that, in the second embodiment of the presentinvention, the nonmagnetic layer may be formed on the surface of thesubstrate and the concave portions may be provided on the nonmagneticlayer.

Third Embodiment

Although the magnetic recording layer has been formed on the servolayers in the second embodiment, conversely the servo layers may beformed on the magnetic recording layer, which will be explained as athird Embodiment of the present invention hereinbelow.

FIG. 11 is a fragmental sectional view showing a magnetic recordingmedium according to the third Embodiment of the present invention. Aplan view of the magnetic recording medium is not shown because it issimilar to that shown in FIG. 4.

Referring to FIG. 11, a magnetic recording medium 21 comprises anonmagnetic substrate 22 made of glass wafer, silicon wafer, aluminumwafer covered by NiP, or the like, a magnetic recording layer 23 made ofCoCr, CoCrPt, CoCrTa, CoNiCr, or the like formed on the nonmagneticsubstrate 22, a nonmagnetic layer 26 made of Cr, Ti, W, SiO₂, or thelike and covering the magnetic recording layer 23, a plurality of servolayers 25 made of CoCr, CoCrPt, CoCrTa, CoNiCr, or the like andsurrounded by the nonmagnetic layer 26 on the magnetic recording layer23, and a protection layer 24 for covering the magnetic recording layer3. Servo patterns 25p are composed of a plurality of separated servolayers 25 and the magnetic recording layer 23 formed on the servo layers25.

The magnetic recording medium 21 has a circular disk shape which hasbeen used in the second embodiment. Like FIG. 4, clock signal patterns27 are formed in the servo signal recording regions B and the servopatterns 25p are arranged between two clock signal patterns 27 in asimilar manner to those in the second embodiment.

The same method as that in the second embodiment may be used to writetracking information into such servo patterns 25p. The trackinginformation written into the servo patterns 25p are read via themagnetic head.

In this case, the magnetic head H is able to read magnetic fieldsgenerated from the servo patterns 25p as the tracking information.Besides, since each servo pattern 25p is formed of the servo layer 25and the magnetic recording layer 23, the tracking signal magnetic fieldsare increased rather than that generated by conventional servo patternswhich are isolated completely.

Furthermore, since the nonmagnetic layer 26 is buried around the servopatterns 25p, a distance between the servo patterns 25p and the magnetichead H can be given by a sum of a flying height of the magnetic head Hand a film thickness of the protection layer 24. As the result, theservo magnetic fields being input into the magnetic head are enhanced toensure reading of the tracking information.

In the magnetic recording medium 21 according to the third Embodiment,if the servo patterns 25p are formed excessively thick, the neighboringnonmagnetic layer 26 also becomes thick. Consequently, a distancebetween the magnetic recording layer 23 and the magnetic head H becomestoo long. It is therefore preferable that, if both the servo layer 25and the magnetic recording layer 23 are formed by the same material, afilm thickness of the servo layer 25 should be set about 2.5 timesthicker than that of the magnetic recording layer 23 based on theexperimental result in FIG. 7B.

Because the nonmagnetic layer 26 is also buried around the servo layers25 in the third Embodiment, evenness of the recording face of themagnetic recording medium 21 can be achieved sufficiently.

Likewise, in the third Embodiment, no data is recorded in the servosignal recording regions B shown in FIG. 4.

A method of forming servo patterns of the above magnetic recordingmedium 21 will be explained to take examples hereinbelow.

FIRST EXAMPLE

First, as shown in FIG. 12A, a hard magnetic layer 31 made of CoCrPt isformed by sputtering on the nonmagnetic substrate 22 to be 5 to 250 nmin thickness. Subsequently, a resist 32 is coated on the hard magneticlayer 31, and then exposed and developed to the hard magnetic layer 31in the regions except for the servo pattern forming regions.

Then, as shown in FIG. 12B, the hard magnetic layer 31 not covered bythe resist 32 is thinned by etching to be 5 to 100 nm in thickness.Thereby, a film thickness of the hard magnetic layer 31 remaining in thetracking pattern forming regions becomes thicker than that in otherregions. The thick hard magnetic layer 31 is used as the servo patterns25p while the thin hard magnetic layer 31 serves as the magneticrecording layer 23.

There are ion milling, sputtering etching, chemical etching, etc. as theetching method, but it would be preferable to use the physical etching(PVD) method such as ion milling.

Next, as shown in FIG. 12C, the nonmagnetic layer 26 made of Cr isformed by sputtering on the entirety of the resultant structure to havea thickness of 5 to 100 nm. Then, the resist 32 is removed by solvent tothus leave the nonmagnetic layer 26 in only the regions not covered bythe resist 32. The nonmagnetic layer 26 is buried around the patternedservo layers 25.

If flashes of the nonmagnetic layer 26 remain on peripheries of theservo layers 25 after the resist 32 is removed, it is necessary toremove the flashes by mechanical polishing, ion milling, sputtering, orthe like and also planalize respective surfaces of the servo layers 25and the nonmagnetic layer 26.

After such planalization process, as shown in FIG. 12D, the protectionfilm 24 is formed on the servo layers 25 and the nonmagnetic layer 26.Thus, the magnetic recording substance with the structure shown in FIG.11 has been finished.

SECOND EXAMPLE

First, as shown in FIG. 13A, the magnetic recording layer 23 made ofCrCoPt and a hard magnetic layer 33 made of CrCoPt are formed bysputtering on the substrate so as to have thicknesses of 5 to 100 nm and5 to 250 nm respectively.

Next, as shown in FIG. 13B, a resist 34 is coated, and then the magneticrecording layer 23 is exposed within the regions excepting the trackingpattern forming regions by exposing and developing the resist 34.

After this, as shown in FIG. 13C, chromium (Cr) is ion-implanted intothe hard magnetic layer 33 located in regions not covered by the resist34, so that the ion implanted regions are changed into nonmagneticlayers 33a. In this event, a depth of ion implantation can be controlledby adjusting ion acceleration energy. With the above, the servo patterns25p are composed of the hard magnetic layer 33 and the magneticrecording layer 23 underlying the resist 34.

Since unevenness of the hard magnetic layer 33 due to ion implantationdoes not occur, planalization process is omissible.

Then, after peeling off the resist 34 by solvent, as shown in FIG. 13D,the protection film 24 covering the servo patterns 25p and thenonmagnetic layers 33a is formed, thereby completing the magneticrecording medium.

In the third Embodiment, it would be understood that the nonmagneticlayer may be formed on the surface of the substrate.

Fourth Embodiment

In the servo regions 45 of the magnetic disk 42 shown in FIG. 2, linearservo patterns 51 which are inclined at a predetermined angle with thetangential direction of the tracks 44, as shown in FIG. 14A, are formedover a plurality of tracks 44. The servo patterns 51 are formed at adistance in the peripheral direction in plural numbers. As shown in FIG.14B, a width W1 of the track 44 is substantially identical to a magneticpole width of the recording head in the magnetic head 50 or a sensewidth of the reproducing head in the magnetic head 50.

The magnetic disk 42 having the servo patterns 51 thereon has asectional structure shown in FIG. 15.

The magnetic disk 42 shown in FIG. 15 comprises a non-magnetic substrate52 made of glass wafer, silicon wafer, aluminum wafer covered with NiP,or the like; an underlying layer 53 made of non-magnetic material suchas Cr or SiO2 on the substrate 52; a magnetic recording layer 54 made ofhard magnetic material such as CoCrTa, CoCrPt, or CoCr on the underlyinglayer 53; and a protection layer 55 covering a magnetic recording layer54. In respect of thickness of these layers 53 to 55, merely by way ofexample, the underlying layer 53 is 50 nm, the magnetic recording layer54 is 20 nm, and the protection layer 55 is 15 nm. Provided that suchconfiguration is employed wherein the underlying layer 53 is omitted,the surface of the substrate 52 serves as the underlying surface for themagnetic recording layer 54.

On the underlying layer 53 which exists in the servo region 45, grooves56 in which a part of the servo patterns 51 are to be buried are formed.A hard magnetic layer 51a such as CoCrTa, CoCrPt, or CoCr is buried inthe grooves 56. Each servo pattern 51 is virtually made up of the hardmagnetic layer 51a buried in one groove 56 and the magnetic recordinglayer 54 formed on the hard magnetic layer 51a. In the servo region 45,since servo information are written into the hard magnetic layer 51a andthe magnetic recording layer 54 formed on the groove 56, data other thanservo information cannot be recorded on the magnetic recording layer 54.The hard magnetic layer 51a may be formed of material similar to ordifferent from the magnetic material constituting the magnetic recordinglayer 54.

In the case that the underlying layer 53 should be omitted, the grooves56 are formed on the substrate 52 and then the hard magnetic layer 51ais buried in the grooves 56.

In turn, a way of writing servo information into the servo patterns 51will be explained hereinbelow.

Writing of servo information is executed the use of a magnetic headshown in FIG. 16A or a permanent magnet shown in FIG. 16B.

As shown in FIG. 16A, in is the case in which case servo information arewritten by using the magnetic head 50, DC magnetic field is generated bythe magnetic head 50 while rotating the circular disk type magnetic disk42, and then desired servo patterns 51 and their peripheral magneticrecording layer 54 are magnetized by the DC magnetic field in the samecircumferential direction.

Similarly, FIG. 16B shows a case in which servo data is written using apermanent magnet. As shown, S and N poles of the permanent magnet 57 arealigned in the circumferential direction and the magnetic disk 42 isthen rotated in this state to magnetize desired servo patterns 51 in thesame direction.

It is similarly applicable to every writing way of servo informationthat all servo patterns 51 are to be magnetized in the samecircumferential direction. The magnetic recording layer 54 locatedwithin regions other than the servo regions 45 is magnetizedconcurrently in writing servo information, nevertheless no problemoccurs in particular since magnetization direction can be changed bywriting data.

As shown in FIG. 17, servo information written as above can be read by amagnetoresistive device (reproducing head) 50a or an inductive device50b. Hence, as shown in FIG. 17, magnetic fields Hs across both ends ofthe servo patterns 51 can be converted into voltage waveforms.

In this event, as shown in FIG. 14B, in respective tracks 44, theposition of the reproducing head 50a is shifted by predetermined pitchesrespectively in the track length direction and the track widthdirection. In other words, linear servo patterns 51 which are arrangedto cross obliquely with a plurality of tracks 44 are equivalent to thecase where the number of split of the servo patterns 30 shown in FIG. 1Awould be increased to reach the limit.

In the magnetic disk 42 in the phase servo system, as shown in FIG. 18,since a first group I and a second group II of the servo patterns 51 areformed symmetrically in the circumferential direction, a trackingcontrol circuit 10a can detect tracking information according to changein phase (interval) β of the servo signal between these groups I and II.

The foregoing servo patterns 51 are not limited to the linear patterns,but as shown in FIG. 19 they may be formed as curved patterns crossingover a plurality of tracks 44. This is because, if the magnetic head 50is swung between the inner periphery and the outer periphery of themagnetic disk 42, change in yaw angle can be reduced smaller when theservo patterns 51 take such curved patterns.

The linear or curved servo patterns 51 mentioned above are present asphysical shape patterns to correspond to change in film thickness.

Therefore, according to such servo patterns 51, such process of writingthe servo patterns 51 at a distance one by one by means of the magnetichead with good precision can be neglected, so that writing time can beshortened. Still further, since density of the servo patterns 51 isdetermined in accordance with change in the film thickness only, thereis no need to consider leakage of the magnetic field or recordingbleeding upon writing the servo information. Therefore, the servopatterns can be achieved with high precision and as a result theprecision of detecting position can be improved.

In addition, since the linear or curved servo patterns 51 are formed tocross over a plurality of tracks 44 obliquely, omission of the patternbecomes hard to occur in contrast to the case where planar shapes of theservo patterns shown in FIG. 1A are employed. As a result, manufacturingyield can be improved.

Next, a way of forming the servo patterns 51 of the above magnetic disk42 (magnetic recording medium) will be explained hereinbelow.

In servo pattern forming steps described later, though the procedure offorming resist patterns comprises two steps of exposing and developingthe resist, a method illustrated in FIG. 20A or FIG. 21A will be adoptedto expose the resist.

FIGS. 20A and 21A illustrate how to fit the circular disk type substrate52, on which the resist 58 is coated, to the rotation shaft of the stepmotor 59 and then expose the resist 58 in this state respectively.

FIG. 20A shows an exposure method using a luminaire 60 and an exposuremask 61. It is not preferable to form the exposure mask 61 so as tocorrespond to the magnetic disk 42 one by one in size since the exposureequipment is increased in volume as a whole and alignment becomes moredifficult. In the meanwhile the servo patterns 51 to be formed on themagnetic disk 42 are arranged repetitiously in the circumferentialdirection. Therefore, the exposure mask 61 having a size of exposurepattern regions 61a which are able to divide the magnetic disk 42 into n(where n is natural number) equal areas in the circumferential directionshould be prepared. Subsequently, the exposure mask 61 is positionedover the substrate 52. In turn, patterns of the exposure mask 61 aretransferred onto the resist 58 by lighting the luminaire 60 positionedover the exposure mask 61 for a predetermined time t1, and then arotation portion of the step motor 59 is rotated by 360/n degree. Aftersuch operations are repeated n times, exposure of the whole surface ofthe resist 58 can be completed. Irradiation of the luminaire 60 anddrive of the step motor 59 can be controlled at timings shown in FIG.20B by the controller 62.

Alignment and focusing of the exposure mask 61 may be carried out eitherevery time when the step motor 59 is stopped or only once before theexposure is commenced.

On the contrary, a laser light source 63 and a laser scanning systemmirror 64 are provided in FIG. 21A. Based on data supplied from apattern data storing portion 65, a controller 66 causes the laser lightsource 63 to turn on and off and causes the laser scanning system mirror64 to swing, thereby scanning the substrate 52 with the laser beam inthe radial direction.

As shown in FIG. 21B, for example, after one scanning of the laser beamin the radial direction has been finished, such operations have beenrepeated that the controller 66 causes the step motor 59 to rotate bypredetermined steps and then causes the laser light source 63 to exposethe resist 58 in the radial direction. When the rotation portion of thestep motor 59 has been rotated up to 360 degree, exposure process of theentire surface of the resist 58 has been completed.

Alternatively, exposure using the laser beam may be effected everycircumferential direction. In this case, as shown in FIG. 21C, the stepmotor 59 is driven continuously at a predetermined rotational speed andat the same time the laser beam irradiation is turned on and off incoincidence with pattern profiles.

By making use of the above exposure method, a method of manufacturingthe magnetic disk 42 having the sectional structure shown in FIG. 15will be explained hereinbelow.

To begin with, as shown in FIG. 22A, an underlying layer 53 is formed ona substrate 52 and then a resist 58 is deposited on the underlying layer53. Subsequently, latent images of the servo patterns are formed byexposing the resist 58 in terms of the exposure method shown in FIG. 20or FIG. 21. Thereafter, as shown in FIG. 22B, openings 58a are formed bydeveloping the resist 58 in respective regions in which the servopatterns 51 are to be formed.

Next, as shown in FIG. 22C, the underlying layer 53 exposed from theopenings 58a of the resist 58 is etched to form the grooves 56. A depthof the groove 56 may be such as to not expose the substrate 52, as shownin FIG. 22C, or else it may be formed to the extent that the substrateis exposed. As the etching method, there are ion milling, sputteretching, chemical etching, and so forth. Provided that silicon is usedas constituting material of the substrate 52, reactive ion etching isapplicable.

Still further, as shown in FIG. 22D, a hard magnetic layer 51a is formedon the entirety by sputtering so as to bury the grooves 56 and then, ifthe resist 58 is removed in virtue of solvent, the hard magnetic layer51a remains only in the grooves 56.

In the next, the underlying layer 53 and the hard magnetic layer 51a areplanarized by means of mechanical polishing, ion milling, or the like.Since the surface opposing to the magnetic head 50 is made flat by thisplanarization, there is no possibility that the magnetic head 50 runningover the surface of the magnetic disk 42 is destroyed by projections.

After such planarization process, as shown in FIG. 22E, when themagnetic recording layer 54 is formed on the hard magnetic layer 51a andthe underlying layer 53 by sputtering to have a thickness of 5 to 100 nmand then a protection film 55 is formed on the magnetic recording layer54, the magnetic disk 42 having the sectional structure shown in FIG. 15has been finished.

Incidentally, lubricant may be coated on the protection layer 55.

Fifth Embodiment

Although in the first embodiment the magnetic recording layer 54 hasbeen formed on the hard magnetic layer 56a as the servo patterns 51,they can be formed so as to put upsidedown. Therefore, anotherembodiment will be explained hereinbelow.

FIG. 23 is a fragmentary sectional view showing a magnetic disk(magnetic recording medium) according to a fifth embodiment of thepresent invention. Since planar shapes and arrangements of the patternsof the hard magnetic layer 51a constituting the servo patterns 51 aresimilar to those have already been explained in the first embodiment,their description is omitted.

In FIG. 23, the magnetic disk 42 comprises a non-magnetic substrate 52made of glass wafer, silicon wafer, aluminum wafer covered with NiPfilm, or the like; an underlying layer 53 made of non-magnetic materialsuch as Cr or SiO2 on the substrate 52; a magnetic recording layer 54made of CoCr, CoCrPt, CoCrTa, CoNiCr, or the like on the underlyinglayer 53; a non-magnetic intermediate layer 67 for covering the magneticrecording layer 54; a hard magnetic layer 51a made of CoCr, CoCrPt,CoCrTa, CoNiCr, or the like, buried in the intermediate layer 67 in theservo regions 45; and a protection layer 55 for covering the hardmagnetic layer 51a and the intermediate layer 67.

In the intermediate layer 67, planar shapes of the grooves 68 to burythe hard magnetic layers 51a therein is the same as those of the servopatterns 51 explained in the first embodiment. The hard magnetic layers51a in the grooves 68 come into contact with the magnetic recordinglayer 54 at the bottom of the grooves 68. The servo patterns 51 arecomposed of the hard magnetic layers 51a in the grooves 68 and themagnetic recording layer 54 directly below the hard magnetic layers 51a.

In such servo patterns 51, a way of writing servo information is similarto that explained in the first embodiment. Servo information writteninto the servo patterns 51 can be read by the magnetic head 50.

Since the non-magnetic intermediate layer 67 is buried around the servopatterns 51, a distance between the servo patterns 51 and the magnetichead 50 can be obtained as a total magnitude of a flying height of themagnetic head 50 and a film thickness of the protection layer 55. As aresult, the servo magnetic field input into the magnetic head 50 can beenhanced to thus ensure reading of tracking information.

In the fifth embodiment, in a similar manner to that shown in FIG. 14Aor FIG. 19, linear or curved servo patterns 51 are formed to cross overa plurality of tracks 44 in the oblique direction and the patterns arethen formed according to change in film thickness in the circumferentialdirection.

Hence, according to such servo patterns 51, like the first embodiment, awriting time can be shortened and high precision patterns can beachieved,.

Still further, since the linear or curved servo patterns 51 are formedto cross over a plurality of tracks 44 at oblique angles, mechanicalstrength of such patterns is enhanced in comparison with isolatedpatterns so that defects of the patterns are hard to occur.

In the fifth embodiment, similarly to that shown in FIG. 14, no dataexcept for servo data is recorded in the magnetic recording layer 54 inthe servo regions 45.

Next, a method of forming the servo patterns 51 having the structureshown in FIG. 23 will be explained hereinbelow.

First, as shown in FIG. 24A, the 50 nm thick underlying layer 53 made ofCr is formed on the substrate 52, then the magnetic recording layer 54made of CoCrPt is formed to have a 20 nm thickness, for example, andthen the intermediate layer 67 made of SiO2 is formed to have athickness of 5 to 20 nm. These layers 53, 54, 67 are formed bysputtering. Subsequently, the resist 58 is coated on the intermediatelayer 67 and then latent images of the servo patterns are formed on theresist 58 by exposing the resist 58 by virtue of the exposure methodshown in FIG. 20A or FIG. 21A.

Next, as shown in FIG. 24B, the resist 58 is patterned by developing theresist 58 to form the openings 58b in respective regions in which theservo patterns are to be formed.

Thereafter, as shown in FIG. 24C, the grooves 68 are formed by removingthe intermediate layers 67 which are not covered with the resist 58 bymeans of etching. As the etching method, ion milling, sputter etching,chemical etching, etc. may be considered.

Then, as shown in FIG. 24D, the 5 to 20 nm thick hard magnetic layer 51amade of CoCrPt is formed on the entirety by sputtering and succeedinglythe hard magnetic layers 51a remain only in the grooves 68 by peelingoff the resist 58 by solvent. The hard magnetic layer 51a and theintermediate layer 67 are planarized by means of polishing, or the like.

As a result, the servo patterns 51 are composed of the hard magneticlayers 51a and the magnetic recording layers 54 just beneath the hardmagnetic layers 51a.

After such planarization process, when the protection film 55 is formedon the hard magnetic layers 51a and the intermediate layer 67, as shownin FIG. 24E, the magnetic disk having the configuration shown in FIG. 23has been accomplished.

The underlying layer 53 is often omitted. Further, lubricant may becoated on the protection layer 55.

Sixth Embodiment

The above linear or curved servo patterns 51 may be formed by patterninga part of the magnetic recording layer 54.

For instance, as shown in FIG. 25A, the underlying layer 53 and themagnetic recording layer 54 of about 20 nm thickness are formed on thesubstrate 52 in order and then the resist 58 is deposited on themagnetic recording layer 54. The resist 58 is then exposed and developedby using the method shown in FIG. 20A or FIG. 21A to pattern the resist58. The resist 58 covers regions other than the servo regions 45.Openings 58c are formed around the servo patterns in the servo regions45.

Subsequently, by removing the magnetic recording layer 54 not coveredwith the resist 58 by means of ion milling, sputter etching, chemicaletching, or the like, the grooves 54a are formed and also the magneticrecording layer 54 other than the servo region 45 is left. The magneticrecording layer 54 remained in the servo region 51 may be used as theservo patterns 51.

In turn, as shown in FIG. 25B, the magnetic recording layer 54 and theservo patterns 51 are covered with the protection film 55 and then thegrooves formed around the servo patterns 51 are filled with theprotection film 55. At that time, the protection film 55 may beplanarized. Furthermore, when lubricant 70 is coated on the protectionfilm 55, the magnetic disk can be finished.

If the servo patterns 51 are to be formed, such a step may be employedthat the magnetic recording layer (hard magnetic layer) 54 is patternedby irradiating the laser beam with high energy to thus obtain servopattern profiles. Irradiation of the laser beam and its timing aresimilar to those shown in FIGS. 21A to 21C.

Though the servo patterns 51 shown in FIG. 25B have been formed bypatterning the magnetic recording layer 54 in the servo regions 45, amethod of forming the servo patterns 51 without patterning of themagnetic recording layer 54 will be explained hereinbelow.

At first, as shown in FIG. 26A, the resist 58 is formed to cover regionsother than the servo regions 45 and the servo pattern forming regions onthe substrate 52. In other words, the resist 58 having windows 58daround the servo pattern forming regions in the servo regions 45 isformed. The windows 58d in the resist 58 are formed through the exposureprocess shown in FIG. 20 or FIG. 21. In turn, the grooves 72 are formedin the substrate 52 by etching the substrate 52 up to a depth of 20 nm,for example, using the resist 58 as a mask. As a result, the hardmagnetic material 71 deposited in the grooves 72 within the servoregions 45 is formed far from the magnetic head 50.

Next, as shown in FIG. 26B, after removing the resist 58 by usingsolvent, the hard magnetic material 71 is formed by sputtering to have athickness of 20 nm, for example. Then, as shown in FIG. 26C, theprotection film 55 is formed on the hard magnetic material 71 andlubricant 70 is then coated thereon.

In the magnetic disk shown in FIG. 26C, provided that the large externalmagnetic field is applied to the hard magnetic material 71 in terms ofthe way shown in FIG. 16A or FIG. 16B, the hard magnetic materials 71 inthe grooves 72 located far away are magnetized weaker than other regionsand in addition they are remote from the reproducing magnetic head 50.As a result, the magnetic fields emitted from the grooves 72 can beextremely reduced. Consequently, in the servo regions 45, convexportions of the hard magnetic material 71 surrounded by the grooves 72act as the servo patterns 51. Besides, the hard magnetic layers 71located in the regions other than the servo regions 45 act as themagnetic recording layer 54.

Change of the magnetic field caused by the servo patterns 51 in theservo regions 45 of the magnetic disk, as shown in FIGS. 25B and 26C,and the servo detection signals are in essential similar to those shownin FIG. 17.

Incidentally, like the third and fourth embodiments, the servo patterns51 shown in FIGS. 25B and 26C have linear or curved planar shapes. And,in the same manner as shown in FIG. 14A or FIG. 19, the servo patterns51 are arranged so as to cross over a plurality of tracks 44 at anoblique angle.

What is claimed is:
 1. A magnetic recording medium, comprising:amagnetic recording layer having first and second surfaces and having aplurality of data signal recording regions and a plurality of servosignal recording regions demarcated so as to be alternately disposed ina circumferential direction; a plurality of servo layers composed of ahard magnetic substance and formed directly on said second surface ofsaid magnetic recording layer, said plurality of servo layers beingdiscontinuously arranged in the circumferential direction in each ofsaid plurality of servo signal recording regions; and a nonmagneticsubstrate supporting the second surface of said magnetic recordinglayer.
 2. The magnetic recording medium according to claim 1, whereinsaid nonmagnetic substrate has a plurality of concave portions in whichsaid plurality of servo layers are buried.
 3. The magnetic recordingmedium according to claim 1, wherein the first surface of aid magneticrecording layer is flattened.
 4. The magnetic recording medium accordingto claim 1, wherein a thickness of each of said plurality of servolayers is at least 2.5 times greater than a thickness of said magneticrecording layer.
 5. The magnetic recording medium according to claim 1,wherein said magnetic recording layer is made of a hard magneticsubstance.
 6. The magnetic recording medium according to claim 1,wherein said plurality of servo layers are made of at least one of CoCr,CoCrPt, CoCrTa, and CoNiCr.
 7. The magnetic recording medium accordingto claim 1, further comprising a plurality of tracks set on saidmagnetic recording layer in a shape of concentric circles along saidcircumferential direction, and wherein said plurality of servo layersare disposed in said plurality of tracks, and individual ones of saidservo layers are spaced from one another by a predetermined amount insaid circumferential direction.
 8. A magnetic recording medium,comprising:a non-magnetic substrate; a plurality of grooves defined insaid substrate; and a magnetic recording layer having upper and lowerfaces, said lower face being formed on said substrate and filling saidgrooves, whereby said magnetic recording layer defines relativelythicker servo recording regions and relatively thinner data signalrecording regions, said servo signal recording regions being demarcatedso as to be alternately disposed in a circumferential direction; whereinsaid grooves being defined at a predetermined oblique angle relative tothe circumferential direction.
 9. The magnetic recording mediumaccording to claim 1, further comprisinga non-magnetic underlying layerinterposed between said substrate and said magnetic layer; and saidgrooves being defined in said underlying layer.